The invention relates to a drive device having a driving machine that operates at a constant speed and is connected mechanically to a working machine via a variable-ratio gear unit which in turn is connected to a variable-ratio drive.
Such drive devices are required for working machines, the rotational speed of which is to be modified during operation.
Published, British Patent Application GB 1 305 393 A discloses a drive device which has a main drive machine which operates at a constant speed. This is connected to a working machine via a variable-ratio gear unit, which is connected to a variable-ratio drive. In each case, an alternating-current electric motor is provided as the main drive machine and as an auxiliary machine. Both are fed from the same current source.
The use of drive machines with different powers, which are fed from different voltage levels, is not possible here. The use of the drive device is therefore very restricted.
Published, European Patent Application EP 0 561 604 A1 describes the connection of a flywheel through a planetary gear unit. The flywheel is driven by a motor and used as the main drive machine. The auxiliary machine used is a servomotor or a hydrodynamic brake.
Japanese Patent Abstract No. 57047054 discloses a system having three adjustable-speed drive motors.
The publication VGB Kraftwerkstechnik [VGB Power Station Technology] 72 (1992), T. Weig and P. Boiger, pages 774 ff., describes a variable-speed drive for boiler feed-water pumps. A driving machine operating at a virtually constant rotational speed is connected to a working machine via a variable-ratio planetary gear unit. The variable-ratio planetary gear unit contains a ring gear with an outer and an inner toothing, one or more planet wheels, the toothings of which engage into the inner toothing of the ring gear, and a sun wheel, the toothing of which engages into that of the planet wheels. The shafts of the planet wheels are mounted on the planet carrier connected to the driving machine and rotate about the sun wheel that is connected to the output shaft. The toothings of the planet wheels and of the sun wheel likewise engage one in the other, thus resulting in rotation of the output shaft. In order to adjust the rotational speed of the working machine, the ring gear can be moved either in or opposite to the main drive direction, thereby achieving respectively a decrease and an increase in the output rotational speed, as compared with the stationary ring gear (nominal rotational speed). A closed hydrostatic circuit with axial piston machines is used for driving this variable-ratio planetary gear unit. An adjusting unit operating at a constant rotational speed and having a variable piston stroke determines the throughflow quantity of the fluid in the hydrostatic circuit, and consequently, the rotational speed of the constant unit having a uniform piston stroke. The constant unit operates as a motor in one direction of rotation or as a pump in the opposite direction and is connected to the outer toothing of the ring gear via a gear train. The adjusting unit is connected via a further gear train to the main drive shaft, from which the adjusting unit receives power when the output rotational speed rises beyond the nominal point or to which it returns power when the output rotational speed falls below the nominal point. In this configuration, the range of adjustment of the rotational speed is limited on account of the existing form of construction, thus restricting the possibility for using the working machine. A critical disadvantage, however, is that high efficiency of the drive system is achieved only at low variable-ratio rotational speeds, since the efficiency of the hydrostatic variable-ratio drive deteriorates rapidly with an increase in variable-ratio rotational speed. Moreover, the device as a whole has a complex configuration, with the result that it is relatively costly to construct.
It is accordingly an object of the invention to provide a drive device which overcomes the above-mentioned disadvantages of the prior art devices of this general type, by which a rotational speed of a working machine can be modified continuously and which, moreover, has a very simple and cost-effective configuration.
With the foregoing and other objects in view there is provided, in accordance with the invention, a drive device for driving a working machine, containing:
a variable-ratio gear unit including at least one planet wheel each having a toothing and a shaft, a carrier for supporting the at least one planet wheel and having a shaft, a sun wheel having a shaft and a toothing, and a ring gear having a rim provided with an inner toothing on an inside and an outer toothing on an outside, the toothing of the at least one planet wheel engages the inner toothing of the ring gear and the toothing of the sun wheel, and the shaft of the sun wheel is provided as an output to which the working machine can be connected mechanically;
at least one main driving machine operating at a constant speed and having a shaft connected to the carrier of the variable-ratio gear unit;
an electronically controlled variable-ratio drive having a frequency converter and an electric motor following the frequency converter, the electric motor has a shaft and a working pinion connected to the shaft, the working pinion is connected mechanically to the ring gear of the variable-ratio gear unit; and
the shaft of the at least one planet wheel, the shaft of the carrier, the shaft of the sun wheel, and the shaft of the electric motor being oriented parallel to one another.
The variable-ratio gear unit of the drive device according to the invention is provided with at least one planet wheel, a carrier for the at least one planet wheel, a sun wheel and a ring gear, a rim of which has toothings on the inside and outside. Toothings of the planet wheels engage in the inner toothing of the ring gear and in the toothing of the sun wheel. Shafts of the planet wheels, the ring gear, the planet carriers and the sun wheel and that of the variable-ratio drive are oriented parallel to one another. The shaft of the sun wheel is used as an output and is connected mechanically to the working machine. This configuration is preferably used in high-speed working machines, of which the speed lies above the speed of the main drive machine. If the speed of the working machine is below that of the main drive machine, the shaft of the main drive machine is connected to the sun wheel. Accordingly, the shaft of the working machine is connected to the planet carrier. The variable-speed drive is controlled electronically. It has a frequency converter that is followed by an electric motor. A working pinion of the electric motor is connected mechanically to the ring gear of the variable-speed drive. The variable-speed variable-ratio drive transmits only relatively low power, depending on the size of the range of adjustment of the rotational speed and on the power characteristic of the working machine. Consequently, as compared with the power of the main drive, only a relatively small and therefore cost-effective frequency converter is necessary. According to the invention, a frequency converter with feedback may also be used. In this case, the output rotational speed may be both increased and decreased in relation to the configuration point, with the ring gear being stationary. In the latter case, the variable-ratio motor operates as a generator. Electrical power is then fed back into the network via the frequency converter.
In accordance with an added feature of the invention, a locking device for locking mechanically one of the carrier and the sun wheel is provided.
In accordance with an additional feature of the invention, a coupling is disposed between the working machine and the variable-ratio gear unit for separating the working machine from the variable-ratio gear unit.
In accordance with another feature of the invention, the frequency converter of the variable-ratio drive has an energy return.
In a variant of the drive device according to the invention, the shaft of the variable-ratio drive is provided with a second pinion that is used as a starting pinion. The latter is configured to be axially displaceable in the same way as the working pinion. The starting pinion can also be engaged into the toothing of a further gearwheel located on the main drive shaft. For this purpose, one or more spur gear stages can also be used, depending on the respective configuration requirements. An outer toothing of the planet carrier may also be used for this purpose. Furthermore, the starting pinion and the working pinion may be identical. In this embodiment of the invention, the motor of the variable-ratio drive may be used for the smooth starting of the main drive and of the working machine and, consequently, the starting motor may be dispensed with. During starting, the working pinion of the variable-ratio drive is not connected to the ring gear. During the starting operation, the ring gear is locked mechanically by a suitable locking device. After the main driving machine has reached a rotational speed to be predetermined, the starting pinion is released from the toothing on the main drive shaft and the supply of energy to the main drive is switched on. The starting pinion may also be disengaged after the supply of energy for the main drive has been switched on. After the disengagement of the starting pinion, the variable-ratio motor is stopped and the working pinion of the variable-ratio drive is engaged into the outer toothing of the stationary ring gear. After the locking of the ring gear has been released, variable-speed variable-ratio operation may commence. The switching operations necessary in the configuration described are therefore to be carried out when the corresponding toothings are at the same circumferential speed or at a standstill. This starting operation presupposes a working machine that is essentially relieved of load. If appropriate, a spur wheel stage may also be interposed. If this load relief is not possible, a suitable coupling must be provided between the output shaft of the drive system and the shaft of the working machine.
A further operating state is achieved if the main drive shaft is locked by a further braking or blocking configuration. In this case, variable-speed operation of the working machine at low power may then be carried out by driving the ring gear by the variable-ratio drive.
If the main driving machine used is an electric motor, this may be connected, together with the electrical variable-ratio drive, to a common alternating-voltage source, for example the electrical mains. The starting device described may also be used for electric main driving machines in the form of asynchronous machines that actually do without a starting motor. It makes it possible to have smaller dimensioning of the electrical wiring and switchgear, since high switch-on currents are avoided.
The drive device according to the invention has a compact configuration and can be assembled completely from standard components. It has high efficiency both under part load and under full load, since the components used all have high efficiencies that do not depend essentially on the rotational speed.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a drive device for driving a working machine, containing:
a variable-ratio gear unit including at least one planet wheel having a shaft and a toothing, a carrier having a shaft and supporting the at least one planet wheel and the carrier is to be connected to the working machine, a sun wheel having a shaft and a toothing, and a ring gear having a rim formed with an inner toothing and an outer toothing, the toothing of the at least one planet wheel engaging the inner toothing of the ring gear and the toothing of the sun wheel;
at least one main driving machine operating at a constant speed and having a shaft connected mechanically to the shaft of the sun wheel;
an electronically controlled variable-ratio drive having a frequency converter, an electric motor following the frequency converter, and a shaft following the electric motor, and the variable-ratio drive connected mechanically to the variable-ratio gear unit; and
the shaft of the at least one planet wheel, the shaft of the carrier, the shaft of the sun wheel, and the shaft of the variable-ratio drive are oriented parallel to one another.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a drive device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.